In recent years, a fuel cell has been attended because of an environment protecting aspect and an energy saving aspect thereof. Generally, the fuel cell has a membrane-electrode assembly (hereinafter, sometimes called “MEA”), and generates power by reaction of an oxygen agent (oxidant) and a fuel. The MEA includes an electrolyte membrane of an ion-conducting property, a fuel pole disposed at one side of the electrolyte membrane, and an oxidant pole disposed at other side of the electrolyte membrane, in a thickness direction thereof. Further, the fuel cell has a fuel distributing plate which forms a passage for supplying a fuel to the fuel pole, and an oxidant distributing plate which forms a passage for supplying the oxidant gas to the oxidant pole. Generally, the fuel distributing plate and the oxidant distributing plate are made of a dense material, not of a porous material, so that the gas may not leak.
In the above fuel cell, an excessive drying of the electrolyte membrane having an ion-conducting property deteriorates the ion conduct property thereof. For this reason, the electrolyte membrane should be prevented from the excessive drying. In view of this, in the conventional fuel cell, the oxidant gas or the fuel has been positively humidified before it is supplied to the fuel cell, by an external humidify apparatus such as a bubbler.
Also, in recent years, a solid high polymer type fuel cell in which the fuel distributing plate and the oxidant distributing plate are made of a porous material having multiple pores, has been developed. In this type fuel cell, a water as a liquid phase is penetrated into the respective pores of the oxidant distributing plate and the fuel distributing plate, and then is supplied to the MEA. The penetrated water in the oxidant distributing plate and that in the fuel distributing plate seal the pores of the distributing plates to prevent gas leakage through the pores.
The Patent Publication No. 1 discloses a fuel cell which includes porous distributing plates each having pores. In this fuel cell, both of the oxidant distributing plate and the fuel distributing plate are made of the porous material, and respective rear surfaces of both distributing plates is provided with a water passage. According to this fuel cell, the water in the respective water passages of the porous oxidant distributing plate and the porous fuel distributing plate can be supplied to the MEA through the pores of the both distributing plates. As a result, excessive drying of the electrolyte membrane can be restrained.
The Patent Publication No. 2 discloses a solid high polymer type fuel cell which includes a conductive and hydrophilic fuel distributing plate, and a conductive and hydrophobic humid water transmitting body. The fuel distributing plate is made of a conductive porous material having a hydrophilic property. The humid water transmitting body is disposed on a rear surface of the fuel distributing plate opposite to the MEA, and is made of a conductive porous material having a hydrophobic property.
According to this solid high polymer type fuel cell, the water as the liquid phase retained in the humid water transmitting body is transmitted toward the MEA through the pores of the fuel distributing plate made of the conductive porous material. Thus, excessive drying of the electrolyte membrane can be restrained by the water. Here, since the fuel distributing plate has the hydrophilic property, the water as the liquid phase effectively transmits through the pores to seal them.
Both of the Patent Publication No. 3 and the Patent Publication No. 4 disclose solid high polymer type fuel cells each of which includes a porous construction of an air distributing plate and a fuel distributing plate. In these fuel cells, a water created in an air pole is allowed to pass through the air distributing plate in a thickness direction thereof, and is supplied to a water passage formed on a rear surface of the air distributing plate. Pressure of a fuel gas in a fuel passage of the fuel distributing plate is adjusted for allowing the water in the water passage to pass through the fuel distributing plate in the thickness direction thereof to the fuel passage. Thus, the fuel in the fuel passage is humidified.    Patent Publication No. 1 Japanese Patent Publication No. 6-338338    Patent Publication No. 2 Japanese Patent No. 2922132 (Japanese Patent Publication No. 8-250130    Patent Publication No. 3 U.S. Pat. No. 5,853,909    Patent Publication No. 4 U.S. Pat. No. 5,700,595